Multiple spacer steps for pitch multiplication

ABSTRACT

Multiple pitch-multiplied spacers are used to form mask patterns having features with exceptionally small critical dimensions. One of each pair of spacers formed around a plurality of mandrels is removed and alternating layers, formed of two mutually selectively etchable materials, are deposited around the remaining spacers. Layers formed of one of the materials are then etched, leaving behind vertically-extending layers formed of the other of the materials, which form a mask pattern. Alternatively, instead of depositing alternating layers, amorphous carbon is deposited around the remaining spacers followed by a plurality of cycles of forming pairs of spacers on the amorphous carbon, removing one of the pairs of spacers and depositing an amorphous carbon layer. The cycles can be repeated to form the desired pattern. Because the critical dimensions of some features in the pattern can be set by controlling the width of the spaces between spacers, exceptionally small mask features can be formed.

REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/144,543, file Jun. 2, 2005, entitled MULTIPLE SPACER STEPS FOR PITCHMULTIPLICATION.

In addition, this application is related to the following: U.S. patentapplication Ser. No. 10/931,772 to Abatchev et al, filed Aug. 31, 2004;U.S. patent application Ser. No. 10/932,993 to Abatchev et al., filedSep. 1, 2004; U.S. patent application Ser. No. 10/931,771 to Tran etal., filed Aug. 31, 2004; U.S. patent application Ser. No. 10/934,317 toSandhu et al., filed Sep. 2, 2004; U.S. patent application Ser. No.10/934,778 to Abatchev et al., filed Sep. 2, 2004; and U.S. PatentProvisional Application No. 60/662,323 to Tran et al., filed Mar. 15,2005, entitled Pitch Reduced Patterns Relative To PhotolithographyFeatures, Attorney Docket No. MICRON.316PR (Micron Ref. No.2004-1130.00/US).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to integrated circuit fabrication and,more particularly, to masking techniques.

2. Description of the Related Art

As a consequence of many factors, including demand for increasedportability, computing power, memory capacity and energy efficiency,integrated circuits are continuously being reduced in size. The sizes ofthe constituent features that form the integrated circuits, e.g.,electrical devices and interconnect lines, are also constantly beingdecreased to facilitate this size reduction.

The trend of decreasing feature size is evident, for example, in memorycircuits or devices such as dynamic random access memories (DRAMs),flash memory, static random access memories (SRAMs), ferroelectric (FE)memories, etc. To take one example, DRAM typically comprises millions ofidentical circuit elements, known as memory cells. In its most generalform, a memory cell typically consists of two electrical devices: astorage capacitor and an access field effect transistor. Each memorycell is an addressable location that can store one bit (binary digit) ofdata. A bit can be written to a cell through the transistor and can beread by sensing charge in the capacitor. By decreasing the sizes of theelectrical devices that constitute a memory cell and the sizes of theconducting lines that access the memory cells, the memory devices can bemade smaller. Storage capacities and speeds can be increased by fittingmore memory cells on a given area in the memory devices.

The continual reduction in feature sizes places ever greater demands onthe techniques used to form the features. For example, photolithographyis commonly used to pattern features, such as conductive lines. Theconcept of pitch can be used to describe the sizes of these features.Pitch is defined as the distance between an identical point in twoneighboring features. These features are typically defined by spacesbetween adjacent features, which spaces are typically filled by amaterial, such as an insulator. As a result, pitch can be viewed as thesum of the width of a feature and of the width of the space on one sideof the feature separating that feature from a neighboring feature.However, due to factors such as optics and light or radiationwavelength, photolithography techniques each have a minimum pitch belowwhich a particular photolithographic technique cannot reliably formfeatures. Thus, the minimum pitch of a photolithographic technique is anobstacle to continued feature size reduction.

“Pitch doubling” or “pitch multiplication” is one proposed method forextending the capabilities of photolithographic techniques beyond theirminimum pitch. A pitch multiplication method is illustrated in FIGS.1A-1F and described in U.S. Pat. No. 5,328,810, issued to Lowrey et al.,the entire disclosure of which is incorporated herein by reference. Withreference to FIG. 1A, a pattern of lines 10 is photolithographicallyformed in a photoresist layer, which overlies a layer 20 of anexpendable material, which in turn overlies a substrate 30. As shown inFIG. 1B, the pattern is then transferred using an etch (preferably ananisotropic etch) to the layer 20, thereby forming placeholders, ormandrels, 40. The photoresist lines 10 can be stripped and the mandrels40 can be isotropically etched to increase the distance betweenneighboring mandrels 40, as shown in FIG. 1C. A layer 50 of spacermaterial is subsequently deposited over the mandrels 40, as shown inFIG. 1D. Spacers 60, i.e., the material extending or originally formedextending from sidewalls of another material, are then formed on thesides of the mandrels 40. The spacer formation is accomplished bypreferentially etching the spacer material from the horizontal surfaces70 and 80 in a directional spacer etch, as shown in FIG. 1E. Theremaining mandrels 40 are then removed, leaving behind only the spacers60, which together act as a mask for patterning, as shown in FIG. 1F.Thus, where a given pitch previously included a pattern defining onefeature and one space, the same width now includes two features and twospaces, with the spaces defined by, e.g., the spacers 60. As a result,the smallest feature size possible with a photolithographic technique iseffectively decreased.

While the pitch is actually halved in the example above, this reductionin pitch is conventionally referred to as pitch “doubling,” or, moregenerally, pitch “multiplication.” Thus, conventionally,“multiplication” of pitch by a certain factor actually involves reducingthe pitch by that factor. The conventional terminology is retainedherein. As can be seen in FIG. 1E, the separation between the spacers 60is partly dependent upon the distance between the mandrels 80. As aresult, the pitch of the spacers 60 can still be limited by theresolution of photolithographic techniques typically used to define themandrels 80. These resolution limits are an obstacle to furtherreductions in feature sizes.

Accordingly, there is a continuing need for methods to form ever smallerfeatures on semiconductor substrates.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a process is provided forsemiconductor processing. The process comprises providing a plurality ofmandrels on a level above a substrate. Spacers are formed on sidewallsof the mandrels. The mandrels and some of the spacers are removed andthe substrate is processed through a mask pattern comprising featuresdefined by a remainder of the spacers.

According to another aspect of the invention, a method is provided forsemiconductor processing. The method comprises forming a first pluralityof spacers by pitch multiplication on a first level and forming a secondplurality of spacers by pitch multiplication on a second level above thefirst level.

According to yet another aspect of the invention, a method is providedfor forming an integrated circuit. The method comprises forming aplurality of spacers of a first material. The spacers are covered bydepositing a layer of a second material on the spacers. A thickness ofthe layer is less than a height of the spacers. A layer of a thirdmaterial is deposited on the layer of the second material. Parts of thelayer of the second material immediately adjacent the spacers areremoved.

According to another aspect of the invention, a method is provided forprocessing semiconductor substrates. The method comprises forming aplurality of spacers by pitch multiplication on a level over asemiconductor substrate. A mask pattern is formed on a mask layerdirectly underlying the spacers by etching through a pattern defined bythe plurality of spacers. The mask pattern comprises one or more maskfeatures disposed between and separated from positions of immediatelyadjacent spacers.

According to yet another aspect of the invention, a method is providedfor processing semiconductor substrates. The method comprises forming aplurality of mandrels over a semiconductor substrate. Spacer material isdeposited around each of the mandrels. A position of one of the mandrelsis measured. A position of spacer material around the one of themandrels is also measured. The mandrels are removed to form a pluralityof spacers. The spacers are trimmed to a desired critical dimension,with the duration of the trim chosen based upon the measured position ofthe one of the mandrels and the measured position of the spacermaterial.

According to another aspect of the invention, a method is provided forsemiconductor processing. The method comprises providing a first set ofmask features. A plurality of spacers is formed over features of thefirst set of mask features. The first set of mask features and theplurality of spacers are consolidated on the same level to form a maskpattern. The plurality of spacers define features in the mask patternbetween features defined by the first set of mask features. A substrateis processed through the mask pattern.

According to yet another aspect of the invention, an integrated circuitis provided. The integrated circuit comprises a plurality of regularlyspaced features in a region of the integrated circuit. The features havea critical dimension of about 50 nm or less and a spacing between themask features is less than about 50 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the Detailed Description ofthe Preferred Embodiments and from the appended drawings, which aremeant to illustrate and not to limit the invention, and wherein:

FIGS. 1A-1F are schematic, cross-sectional side views of a sequence ofmasking patterns for forming conductive lines, in accordance with aprior art pitch doubling method;

FIG. 2 is a schematic cross-sectional side view of a partially formedintegrated circuit, in accordance with preferred embodiments of theinvention;

FIG. 3 is a schematic cross-sectional side view of the partially formedintegrated circuit of FIG. 2 after forming lines in a photoresist layer,in accordance with preferred embodiments of the invention;

FIG. 4 is a schematic cross-sectional side view of the partially formedintegrated circuit of FIG. 3 after widening spaces between lines in thephotoresist layer, in accordance with preferred embodiments of theinvention;

FIG. 5 is a schematic, cross-sectional side view of the partially formedintegrated circuit of FIG. 4 after etching through a first hard masklayer, in accordance with preferred embodiments of the invention;

FIG. 6 is a schematic, cross-sectional side view of the partially formedintegrated circuit of FIG. 5 after transferring a pattern from the hardmask layer to a temporary layer to form a pattern of mandrels in thetemporary layer, on a first level, in accordance with preferredembodiments of the invention;

FIG. 7 is a schematic, cross-sectional side view of the partially formedintegrated circuit of FIG. 6 after a hard mask layer removal, inaccordance with preferred embodiments of the invention;

FIG. 8 is a schematic, cross-sectional side view of the partially formedintegrated circuit of FIG. 7 after depositing a layer of a spacermaterial, in accordance with preferred embodiments of the invention;

FIG. 9 is a schematic, cross-sectional side view of the partially formedintegrated circuit of FIG. 8 after a spacer etch, in accordance withpreferred embodiments of the invention;

FIG. 10 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 9 after forming a protective layerover and around the spacers and mandrels, in accordance with preferredembodiments of the invention;

FIG. 11 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 10 after patterning the protectivelayer, in accordance with preferred embodiments of the invention;

FIG. 12 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 11 after a removal of selectedspacers, in accordance with preferred embodiments of the invention;

FIG. 13 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 12 after removing the protective layerand the mandrels, in accordance with preferred embodiments of theinvention;

FIG. 14A is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 13 after depositing a planarizinglayer and a hard mask layer, respectively, over the mandrels, inaccordance with preferred embodiments of the invention;

FIG. 14B is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 14A after depositing a secondtemporary layer, a hard mask layer and a photodefinable layer,respectively, in accordance with preferred embodiments of the invention;

FIG. 15 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 14B after forming a pattern ofmandrels in the second temporary layer, on a second level, in accordancewith preferred embodiments of the invention;

FIG. 16 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 15 after depositing a spacer materialaround the mandrels and conducting an incomplete spacer etch, inaccordance with preferred embodiments of the invention;

FIG. 17 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 16 after trimming the spacer material,in accordance with preferred embodiments of the invention;

FIG. 18 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 17 after selectively removing mandrelsand selected spacers on the second level, in accordance with preferredembodiments of the invention;

FIG. 19 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 18 after etching the remaining spacerson the second level to desired dimensions, in accordance with preferredembodiments of the invention;

FIG. 20 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 19 after forming spacers on a thirdlevel, in accordance with preferred embodiments of the invention;

FIG. 21 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 22 after selectively etching a hardmask layer, in accordance with preferred embodiments of the invention;

FIG. 22 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 21 after consolidating the spacerpatterns on the second and third levels on the first level, inaccordance with preferred embodiments of the invention;

FIG. 23 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 24 after selectively etching a hardmask layer, in accordance with preferred embodiments of the invention;

FIG. 24 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 23 overlying a primary masking layer,in accordance with preferred embodiments of the invention;

FIG. 25 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 24 after transferring a pattern formedby spacers in the first, second and third levels into the primarymasking layer, in accordance with preferred embodiments of theinvention;

FIG. 26 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 12 after removing the protective layerand the mandrels, in accordance with preferred embodiments of theinvention;

FIG. 27 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 26 after depositing a layer of amaterial selectively etchable relative to the spacers over the spacers,in accordance with other preferred embodiments of the invention;

FIG. 28 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 27 after depositing a layer of spacermaterial, in accordance with other preferred embodiments of theinvention;

FIG. 29 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 28 after a spacer etch, in accordancewith other preferred embodiments of the invention;

FIG. 30 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 29 after depositing another layer ofthe selectively etchable material, in accordance with preferredembodiments of the invention;

FIG. 31 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 30 after depositing another layer ofspacer material, in accordance with preferred embodiments of theinvention;

FIG. 32 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 31 after a planarization step, inaccordance with preferred embodiments of the invention;

FIG. 33 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 32 after etching the selectivelyetchable material, in accordance with preferred embodiments of theinvention;

FIG. 34 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 33 overlying a primary masking layer,in accordance with preferred embodiments of the invention; and

FIG. 35 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 34 after transferring the patternformed by the spacer material into the primary masking layer, inaccordance with preferred embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In preferred embodiments of the invention, in a masking process forreducing feature sizes, the distance between features in a mask patternis decoupled from the formation of that particular feature. For example,the distance between spacers is decoupled from the width of the mandrelsused to form the spacers. Advantageously, exceptionally closely spacedmask features or mask features can be formed.

In some preferred embodiments, mask features, such as spacers, areformed on a first level and additional mask features are formed on oneor more higher levels in the lateral space between the features on thefirst level. All the mask features are then consolidated on a singlelevel above a substrate, which can be patterned using the consolidatedmask features.

For example, in preferred embodiments, spacers are formed at thesidewalls of mandrels on a first level. The mandrels and a plurality ofspacers, preferably one of each pair of spacers formed around a mandrel,are removed, leaving a pattern of “single spacers” that have a pitchsubstantially equal to the pitch of the mandrels. A temporary layer isthen formed around the spacers.

On a second level over these spacers, mandrels are formed and spacersare formed around the mandrels. The mandrels and a plurality of spacers,preferably every other spacer, on the second level are removed to formanother pattern of single spacers over the pattern of spacers on thefirst level. These cycles of spacer formation and mandrel and spacerremoval can be repeated on successively higher levels, as desired. Forexample, these cycles can be terminated before newly formed singlespacers overlap regions of previously formed spacers.

Advantageously, the lateral separation between spacers is based partlyon photo-overlay capabilities and the ability to form mandrels andspacers at desired positions. Because photo-overlay capabilities can bebetter than the resolutions of the techniques used to pattern themandrels, the distance between spacers can be reduced in comparison tousing photolithographically defined mandrels to determine the spacingbetween spacers. Moreover, because spacers on successively higher levelsare formed independent of spacers on lower levels, the spacers on thehigher levels can be independently trimmed as necessary to moreaccurately achieve a desired critical dimension and/or spacing.

In other preferred embodiments, the spacing between the single spacersis determined by depositing layers of a second material around thespacers. Preferably, the second material is selectively etchablerelative to the material forming the spacers. Vertically extendinglayers of spacer material (or other material with similar etchselectivity) and material(s) selectively etchable relative to thespacers are alternatingly deposited. These layers are then exposed andetched, leaving behind, e.g., only features protected by the verticallyextending spacer material. Advantageously, the spacing between thespacer material is determined by the thickness of the layers of theother material(s). This thickness can be precisely controlled bycontrolling the deposition of the material, thereby allowing goodcontrol of the spacing of the spacer material.

Reference will now be made to the Figures, wherein like numerals referto like parts throughout. It will be appreciated that the Figures arenot necessarily drawn to scale.

Initially, a sequence of layers of materials is formed to allowformation of the spacers on a first level over a substrate.

FIG. 2 shows a cross-sectional side view of a partially formedintegrated circuit 100. While the preferred embodiments can be used toform any integrated circuit, they are particularly advantageouslyapplied to form devices having arrays of electrical devices, includingmemory cell arrays for volatile and non-volatile memory devices such asDRAM, ROM or flash memory, including NAND flash memory. Consequently,the integrated circuit 100 can preferably be a memory chip or a logic orprocessor with embedded memory or a gate array.

With continued reference to FIG. 2, various masking layers 120-150 arepreferably provided above a substrate 110. The layers 120-150 will beetched to form a mask for patterning the substrate 110, as discussedbelow. The materials for the layers 120-150 overlying the substrate 110are preferably chosen based upon consideration of the chemistry andprocess conditions for the various pattern forming and patterntransferring steps discussed herein. Because the layers between atopmost selectively definable layer 120 and the substrate 110 preferablyfunction to transfer a pattern derived from the selectively definablelayer 120 to the substrate 110, the layers 130-150 between theselectively definable layer 120 and the substrate 110 are preferablychosen so that they can be selectively etched relative to other exposedmaterials. It will be appreciated that a material is consideredselectively, or preferentially, etched when the etch rate for thatmaterial is at least about 5 times greater, preferably at least about 10times greater, more preferably at least about 20 times greater and, mostpreferably, at least about 40 times greater than that for surroundingmaterials. Because a goal of the layers 120-150 overlying the substrate110 is to allow well-defined patterns to be formed in that substrate110, it will be appreciated that one or more of the layers 120-150 canbe omitted or substituted if suitable other materials, chemistriesand/or process conditions are used. For example, the layer 130 can beomitted in some embodiments where the resolution enhancement propertiesof that layer, as discussed below, are not desired. In otherembodiments, discussed further below, additional masking layers can beadded between the layer 150 and the substrate 110 to form a mask havingimproved etch selectivity relative to the substrate 110. Exemplarymaterials for the various layers discussed herein include silicon oxide,silicon nitride, silicon, amorphous carbon, dielectric antireflectivecoatings (DARC, silicon rich silicon oxynitride), and organic bottomantireflective coatings (BARC), each of which can be selectively etchedrelative to at least 2 or 3 of the other materials, depending upon theapplication.

In addition to selecting appropriate materials for the various layers,the thicknesses of the layers 120-150 are preferably chosen dependingupon compatibility with the etch chemistries and process conditionsdescribed herein. For example, when transferring a pattern from anoverlying layer to an underlying layer by selectively etching theunderlying layer, materials from both layers are removed to some degree.Preferably, the upper layer is thick enough so that it is not worn awayover the course of the pattern transfer.

The selectively definable layer 120 overlies a first hard mask, or etchstop, layer 130, which overlies a temporary layer 140, which overlies asecond hard mask, or etch stop, layer 150, which overlies the substrate110 to be processed (e.g., etched) through a mask. The selectivelydefinable layer 120 is preferably photodefinable, e.g., formed of aphotoresist, including any photoresist known in the art. For example,the photoresist can be any photoresist compatible with 157 nm, 193 nm,248 nm or 365 nm wavelength systems, 193 nm wavelength immersionsystems, extreme ultraviolet systems (including 13.7 nm systems) orelectron beam lithographic systems. Examples of preferred photoresistmaterials include argon fluoride (ArF) sensitive photoresist, i.e.,photoresist suitable for use with an ArF light source, and kryptonfluoride (KrF) sensitive photoresist, i.e., photoresist suitable for usewith a KrF light source. ArF photoresists are preferably used withphotolithography systems utilizing relatively short wavelength light,e.g., 193 nm. KrF photoresists are preferably used with longerwavelength photolithography systems, such as 248 nm systems. In otherembodiments, the layer 120 and any subsequent resist layers can beformed of a resist that can be patterned by nano-imprint lithography,e.g., by using a mold or mechanical force to pattern the resist.

The material for the first hard mask layer 130 preferably comprises aninorganic material. Exemplary materials include silicon oxide (SiO₂),silicon or a dielectric anti-reflective coating (DARC), such as asilicon-rich silicon oxynitride. Preferably, the first hard mask layer130 is a dielectric anti-reflective coating (DARC). Using DARCs for thefirst hard mask layer 130 can be particularly advantageous for formingpatterns having pitches near the resolution limits of aphotolithographic technique. The DARCs can enhance resolution byminimizing light reflections, thus increasing the precision with whichphotolithography can define the edges of a pattern.

The temporary layer 140 is preferably formed of amorphous carbon, which,as noted above, offers very high etch selectivity relative to thepreferred hard mask materials. More preferably, the amorphous carbon isa form of amorphous carbon that is highly transparent to light and thatoffers further improvements for photo alignment by being transparent tothe wavelengths of light used for such alignment. Deposition techniquesfor forming such transparent carbon can be found in A. Helmbold, D.Meissner, Thin Solid Films, 283 (1996) 196-203, the entire disclosure ofwhich is incorporated herein by reference.

The material for the second hard mask layer 150 is preferably chosenbased upon the material used for the spacers and for the underlyingsubstrate 110. Where the spacer material is an oxide, the second hardmask layer 150 preferably comprises a dielectric anti-reflective coating(DARC) (e.g., a silicon oxynitride), silicon or aluminum oxide (Al₂O₃).In addition, a bottom anti-reflective coating (BARC) (not shown) canoptionally be used to control light reflections. In the illustratedembodiment, the second hard mask layer 150 comprises amorphous silicon.In other cases, where the substrate 110 comprises silicon, the secondhard mask layer 150 can be any material, e.g., Al₂O₃, preferably havinggood etch selectivity relative to silicon.

The various layers discussed herein can be formed by various methodsknown in the art. For example, spin-on-coating processes can be used toform photodefinable layers, BARC, and spin-on dielectric oxide layers.Various vapor deposition processes, such as chemical vapor deposition,can be used to form hard mask layers.

Next, a pattern of spacers is formed by pitch multiplication. Withreference to FIG. 3, a pattern comprising spaces or trenches 122, whichare delimited by photodefinable material features 124, is formed in thephotodefinable layer 120. The trenches 122 can be formed by, e.g.,photolithography with 248 nm or 193 nm light, in which the layer 120 isexposed to radiation through a reticle and then developed. After beingdeveloped, the remaining photodefined material forms mask features suchas the illustrated lines 124 (shown in cross-section only).

As shown in FIG. 4, the photoresist lines 124 can be etched using anisotropic etch to “shrink” those features to adjust their widths. Theextent of the etch is preferably selected so that the widths of themodified lines 124 a are substantially equal to the desired spacingbetween the later-formed spacers 175 (FIG. 9), as will be appreciatedfrom the discussion below. Suitable etches include etches using anoxygen-containing plasma, e.g., a SO₂/O₂/N₂/Ar plasma, a Cl₂/O₂/Heplasma or a HBr/O₂/N₂ plasma. For example, the width of the lines 124can be reduced from about 80-120 nm to about 40-70 nm. Advantageously,the width-reducing etch allows the lines 124 a to be narrower than wouldotherwise be possible using the photolithographic technique used topattern the photodefinable layer 120. In addition, the etch can smooththe edges of the lines 124 a, thus improving the uniformity of thoselines. While the critical dimensions of the lines 124 a can be etchedbelow the resolution limits of the photolithographic technique, it willbe appreciated that this etch does not alter the pitch of the spaces 122a and lines 124 a, since the distance between identical points in thesefeatures remains the same.

With reference to FIG. 5, the pattern in the (modified) photodefinablelayer 120 a is transferred to the hard mask layer 130. This transfer ispreferably accomplished using an anisotropic etch, such as an etch usinga fluorocarbon plasma, although a wet (isotropic) etch may also besuitable if the hard mask layer 130 is thin. Preferred fluorocarbonplasma etch chemistries include CFH₃, CF₂H₂ and CF₃H.

With reference to FIG. 6, the pattern in the photodefinable layer 120 aand the hard mask layer 130 is transferred to the temporary layer 140 toform mandrels 145. A layer 170 of spacer material (FIG. 8) will later bedeposited on the mandrels 145. It has been found that the temperaturesused for spacer material deposition (which is preferably conformal, suchthat chemical vapor deposition or atomic layer deposition are preferred)are typically too high for photoresist to withstand. Thus, the patternis preferably transferred from the photodefinable layer 120 a to thetemporary layer 140, which is formed of a material that can withstandthe process conditions for spacer material deposition and etching,discussed below. In addition to having higher heat resistance thanphotoresist, the material forming the temporary layer 140 is preferablyselected such that it can be selectively removed relative to thematerial for the spacers 175 (FIG. 9) and the underlying etch stop layer150. As noted above, the layer 140 is preferably formed of amorphouscarbon and, more preferably, transparent carbon.

The pattern in the modified photodefinable layer 120 a is preferablytransferred to the temporary layer 140 using a O₂-containing plasma,e.g., a plasma containing SO₂, O₂ and Ar. Other suitable etchchemistries include a Cl₂/O₂/SiCl₄ or SiCl₄/O₂/N₂ or HBr/O₂/N₂/SiCl₄containing plasma. Advantageously, the SO₂-containing plasma is used asit can etch carbon of the preferred temporary layer 140 at a rategreater than 20 times and, more preferably, greater than 40 times therate that the hard mask layer 130 is etched. A suitable SO₂-containingplasma is described in U.S. patent application Ser. No. 10/931,772 toAbatchev et al, filed Aug. 31, 2004, the entire disclosure of which isincorporate herein by reference. It will be appreciated that theSO₂-containing plasma can simultaneously etch the temporary layer 140and also remove the photoresist layer 120 a. The resulting lines 124 b,separated by spaces 122 b, constitute the placeholders or mandrels alongwhich a pattern of spacers 175 (FIG. 9) will be formed.

With reference to FIG. 7, the hard mask layer 130 can be selectivelyremoved to facilitate later spacer formation by leaving the mandrels 145exposed for subsequent etching (FIG. 12). The hard mask layer 130 can beremoved using a buffered oxide etch (BOE), which is a wet etchcomprising HF and NH₄F.

Next, as shown in FIG. 8, a layer 170 of spacer material is preferablyblanket deposited conformally over exposed surfaces, including the hardmask layer 150 and the tops and sidewalls of the mandrels 145. Thespacer material can be any material that can act as a mask fortransferring a pattern to the underlying hard mask layer 150. The spacermaterial preferably: 1) can be deposited with good step coverage; 2) canbe deposited at a temperature compatible with the mandrels 145; and 3)can be selectively etched relative to the mandrels 145 and underlyinghard mask layer 150. Preferred materials include silicon, silicon oxidesand silicon nitrides. In the illustrated embodiment, the spacer materialis silicon oxide, which provides particular advantages in combinationwith other selected materials of the masking stack.

Preferred methods for spacer material deposition include chemical vapordeposition, e.g., using O₃ and TEOS to form silicon oxide, and atomiclayer deposition (ALD), e.g., using a self-limitingly deposited siliconprecursor and an oxygen precursor to form silicon oxide. The thicknessof the layer 170 is preferably determined based upon the desired widthof the spacers 175 (FIG. 9). Preferably, the step coverage is about 80%or greater and, more preferably, about 90% or greater.

With reference to FIG. 9, the silicon oxide spacer layer 170 is thensubjected to an anisotropic etch to remove spacer material fromhorizontal surfaces 180 of the partially formed integrated circuit 100.Such a directional etch, also known as a spacer etch, can be performedusing a fluorocarbon plasma, e.g., containing CF₄/CHF₃, C₄F₈/CH₂F₂ orCHF₃/Ar plasma. While shown for ease of illustration havingapproximately the same width as the mandrels 145, the spacers 175 canhave a smaller width than the mandrels 145.

Next, some of the spacers 175, and preferably every other spacer 175, isremoved. With reference to FIG. 10, a protective material 185 isdeposited around and over the spacers 175 and the mandrels 145. Theprotective material 185 is preferably a photodefinable material such asphotoresist. Optionally, an anti-reflective coating (not shown) can beprovided under the layer 185 to improve photolithography results. Thephotoresist and the anti-reflective coating can be deposited usingvarious methods known in the art, including spin-on-coating processes.

With reference to FIG. 11, the protective layer 185 is patterned, e.g.,by photolithography, to protect desired spacers 175 from a subsequentspacer removal step. In the illustrated embodiment, one of each pair ofspacers 175 formed around a mandrel 145 is left exposed for removal.

With reference to FIG. 12, the exposed spacers 175 are etched away.Where the spacers 175 comprise silicon oxide, preferred etch chemistriesinclude a fluorocarbon etch or the spacers 175 can be etched using a wetchemistry, e.g., a buffered oxide etch. It will be appreciated thatspacers 175 may be removed in some regions of the integrated circuit100, but are not removed in other regions, depending upon the desiredpattern etched into the protective layer 185.

With reference to FIG. 13, the protective layer 185 and the mandrels 145are preferably selectively removed. Where the material forming theprotective layer 185 is an organic material such as photoresist or BARC,preferred etch chemistries include anisotropic etches, such as with aSO₂-containing plasma. Advantageously, these chemistries can also removethe mandrels 145, which are formed of carbon in the illustratedembodiment. The partially formed integrated circuit 100 can also besubjected to an ash process to remove the protective layer 185 and themandrels 145. It will be appreciated that the protected spacers 175 arenot attacked during this removal step and that the substrate 110 isprotected by the second hard mask layer 150. Thus, a pattern of “singlespacers” 175 are formed on a first level over the substrate 110.

It will be appreciated that the spacers 175 are spaced sufficiently farapart to accommodate other mask features in the space between thespacers 175. In the illustrated embodiment, if the width of the spacers175 is considered to be ½ F, the separation between spacers 175 is about7/4 F.

A sequence of layers is then deposited to allow formation of additionalspacers in the space between the spacers 175 on a second level over thespacers 175 and the substrate 110. With reference to FIG. 14A, aplanarizing layer 200 is deposited around the single spacers 175 and ahard mask layer 210 is deposited over the second temporary layer 200. Ifnecessary, the layer 200 can be planarized by, e.g., chemical mechanicalpolishing (CMP) before forming the hard mask layer 210. Typically, ifthe material is a spin-on material (e.g., resist, SOD, BARC), CMP is notnecessary.

The planarizing layer 200 is preferably formed of a material selectivelyetchable relative to both the spacers 175 and the layer 150. The hardmask layer 210 is preferably formed of a material selectively etchablerelative to the planarizing layer 200. For example, the planarizinglayer 200 can be formed of amorphous carbon, while the hard mask layer210 can be formed of a DARC or amorphous silicon.

With reference to FIG. 14B, a sequence of layers 220-240 can bedeposited to allow formation of additional spacers over the hard masklayer 210. For example, as discussed above with reference to FIG. 2, thesecond temporary layer 220 can comprise amorphous carbon, the hard masklayer 230 can comprise silicon oxide (SiO₂), silicon or a DARC, and thephotodefinable layer 240 can comprise a photoresist.

Preferably, applying again the steps discussed above with reference toFIGS. 2-7, a pattern of mandrels 245 are formed in the layer 220, asshown in FIG. 15. With reference to FIG. 16, spacer material 270 isdeposited around the mandrels 245. As noted above, the spacer material270 can be any material having deposition and etch properties compatiblewith the other materials used herein. Depending on the identity of thespacer material 270, the spacer material 270 may be deposited by atomiclayer deposition, as discussed above.

In the illustrated embodiment, the spacer material 270 is silicon oxideand is deposited by chemical vapor deposition using O₃ and TEOS. Asuitable deposition system is Applied Materials' Producer® HARP™ system.After the deposition, the spacer material 270 may extend over thesurface of the hardmask layer 210 between two mandrels 245. Where thisoccurs, the spacer material 270 can be subjected to an optionallyincomplete spacer etch, leaving only a thin spacer material layer 271over the mandrels 245 and the hard mask layer 210. In other embodiments,the spacer material layer 271 can be completely absent. FIG. 16 showsthe spacer material 270 after an incomplete spacer etch.

With continued reference to FIG. 16, the width of the deposited spacermaterial 270 is preferably chosen to exceed the desired width of thespacer 275 (FIG. 19) that will be formed from the spacer material 270.The excess width at this point can be provided by excess depositionand/or an incomplete spacer etch. This excess spacer width allows amargin for the width and position of the resulting spacers 275 to befine-tuned by trim etching, thereby increasing the uniformity of thespacers 275 and the precision with which the spacers 275 are placed.

It will be appreciated that due to various factors, including errors inphoto-alignment and the resolution of photolithography methods, themandrels 245 may be misaligned by a particular margin. This misalignmentcan cause misalignments in the ultimately formed spacers 275 (FIG. 19)relative to their desired positions. Consequently, the mandrels 245 arepreferably positioned and sized so that the spacer material 270 extendsover an area greater than the desired position of the spacers 275. Theposition of spacer material 270 can then be measured and etched, asnecessary, to form spacers 275 having the desired critical dimensionsand positioning.

With continued reference to FIG. 16, the mandrel 245 is laterally spacedfrom a reference point, the spacer 175 _(R), by a lateral distance X (asmeasured from the edge of the mandrel 245 closest to the spacer 175_(R)). Similarly, the spacer material 270 is laterally spaced from thespacer 175 _(R) by a lateral distance Y (as measured from the edge ofthe spacer material 270 closest to the spacer 175 _(R)). These positionsare measured using metrology tools, as known in the art. The width ofthe spacer material 270 is X−Y.

Depending on the width of the spacer material and its spacing from thespacer 175 _(R), the spacer material is subjected to a first trim etchto approximately center the structures 270 on the desired positions ofthe soon to be formed spacers 275 (FIG. 19), as shown in FIG. 17. Theposition of the spacer material 270 before the etch is shown in dottedlines. Note that the “centering” does not necessarily position thestructures 270 exactly centered on the positions of the spacers 275(FIG. 19). Rather, the centering preferably positions the spacers 275 soas to account for the slightly different etch rates, E_(L) and E_(R), atdifferent sides of the spacer. For example, where E_(R) is greater thanE_(L), the structures 270 may be slightly skewed to the right of beingexactly centered on the spacers 275 (FIG. 19).

The first trim etch is preferably an isotropic etch. Exemplary isotropicetch chemistries for silicon oxide spacer material include SF₆ and/orNF₃. If as shown in FIG. 16, the spacer etch was incomplete, the firsttrim etch removes the thin bridging layers 271 of spacer material. Afterthe first trim etch, the spacer material 270 is laterally spaced fromthe spacer 175 _(R) by Y′.

As shown in FIG. 18, the mandrels 245 and spacer material 270 on oneside of each mandrel 245 are then removed, forming spacers 275. Thisremoval can be accomplished as discussed above with reference to FIGS.10-13.

Now preferably approximately centered on their desired positions, thespacers 275 are subjected to another isotropic trim etch to form spacers275 having the desired width. Unlike the trim etch with the mandrels 245in place, this second trim etch affects both edges of the exposedspacers 275. The duration, t, of this second trim etch can be calculatedbased upon the following relationship:

(X−Y′)−E _(L) t−E _(R) t=W=X″−Y″

where: X is the lateral distance from the right edge of the spacer 275to the spacer 175 before second trim etch,

Y′ is the lateral distance from the left edge of the spacer 275 to thespacer 175 before second trim etch,

E_(L)t is the etch rate at the left side of the spacer 275,

E_(R)t is the etch rate at the right side of the spacer 275,

W is the desired width for the spacer 275 after etching,

X″ is the lateral distance from the left edge of the spacer 275 to thespacer 175 after etching, and

Y″ is the lateral distance from the right edge of the spacer 275 to thespacer 175 after etching.

It will be appreciated that X and Y′ are typically measured values, asdiscussed above. Alternatively, Y′ can be calculated based upon themeasured value for Y, the etch rate of the first trim etch and theduration of the first trim etch. E_(L) and E_(R) are experimentallydetermined values for a given etch chemistry under particular processconditions. The etch rates for the left and right sides of the spacers275 can be different due to the different geometries of those sides;that is, because one side extends vertically and because the other sideis at an angle to the horizontal, the rate at which each side islaterally displaced by an etch can vary. W is a desired value, e.g., 50nm. Thus, the second trim etch time t can be calculated by the followingequation:

$t = {\frac{( {X - Y^{\prime}} ) - W}{E_{L} + E_{R}}.}$

Having calculated time t, the spacers 275 are subjected to an isotropictrim etch for that time t. With reference to FIG. 19, the position ofthe spacers 275 before the etch is shown in dotted lines. A suitablechemistry for the second trim etch is a fluorocarbon etch, comprising,e.g., C_(x)F_(y) or C_(x)F_(y)H_(z). After the second trim etch, thelateral distance from the left edge of the spacer 275 to the spacer 175is X″ and the lateral distance from the right edge of the spacer 275 tothe spacer 175 is Y″.

With reference to FIG. 20, another planarizing layer 300 is formedaround the spacers 275 and a hard mask layer 310 is formed over theplanarizing layer 300. The planarizing layer can be formed of, e.g.,amorphous carbon and the hard mask layer 310 can be formed of, e.g.,silicon or a DARC. It will be appreciated that the layer 300 can beplanarized by CMP, as discussed above. The steps discussed withreference to FIGS. 14A-19 can then be performed again to leave a patternof third spacers 375 on a third level, above the second spacers 275.

Next, a pattern defined by all the spacers 175, 275 and 375 isconsolidated on a single level. As shown in FIG. 21, spacers 375 areused as a mask to pattern the hard mask layer 310. The hard mask layeris preferably selectively etched relative to the spacers 375 and theplanarizing layer 300 using an anisotropic etch, such as an etch using afluorocarbon plasma, where the layer 310 comprises a DARC. Preferredfluorocarbon plasma etch chemistries include CFH₃, CF₂H₂ CF₃H, C₄F₈,C₃F₆ and/or CF₄.

The planarizing layer 300 can then be selectively and anisotropicallyetched, as shown in FIG. 22. Where the planarizing layer 300 is formedof amorphous carbon, preferred etch chemistries include a SO₂-containingplasma, e.g., a plasma containing SO₂, O₂ and Ar.

As with the layers 300 and 310, the hard mask layer 210 and theplanarizing layer 200, respectively, are subjected to selectiveanisotropic etches, thereby consolidating a pattern formed by thespacers 175, 275 and 375 on the first level. The resulting structure isshown in FIG. 23.

In some embodiments, particularly where the substrate 110 can be etchedwith good selectivity relative to the hard mask layer 150, the hard masklayer 150 can be used as a mask to etch the substrate 110. The patternformed by the spacers 175, 275 and 375 can be transferred from the firstlevel to the hard mask layer 150 by using an anisotropic etch with HBrand Cl₂-containing plasma to etch the layer 150 through that patternformed by the spacers 175, 275 and 375. Alternatively, at each transferstep, the spacer patterns can be transferred to its immediatelyunderlying hard mask and the spacers removed prior to transferring intothe underlying protective layers. In this way, the aspect ratios of theresultant mask features (FIG. 23 or 24) can be reduced prior to transferto the substrate. Optionally, one or more of the features, such as thespacers 175, 275, 375, overlying the layer 160 can be removed to reducethe aspect ratio of mask features before etching the substrate 110.

In other embodiments, especially where the substrate 110 is difficult toetch, intervening layers of masking material can be formed between thehard mask layer 150 and the substrate 110. For example, with referenceto FIG. 24, additional layers 155 and 160 can be provided, as discussedin U.S. Patent Provisional Application No. 60/662,323 to Tran et al.,filed Mar. 15, 2005, entitled Pitch Reduced Patterns Relative ToPhotolithography Features, Attorney Docket No. MICRON.316PR (Micron Ref.No. 2004-1130.00/US), the entire disclosure of which is incorporatedherein by reference. The layer 155 allows for a pattern-cleaning step toremove any polymerized organic residue that may be present as the resultof previous etch processes. After the cleaning step, a well-definedpattern can be transferred to the layer 160. The layer 160 is preferablyformed of amorphous carbon, which is advantageously resistant to manyetch chemistries for removing silicon materials in the substrate 110. Asshown in FIG. 25, the pattern defined by the spacers 175, 275 and 375can be transferred to the layer 160, which then serves as the primarymask for patterning the substrate 110. Advantageously, due to theavailability of extreme selectivity when etching amorphous carbon, apatterned hard mask layer 150 can be used after removal of spacers totransfer the pattern with lower and more uniform aspect ratio featuresin the hard mask.

FIGS. 26-35 illustrate other methods for forming a mask pattern,according to other preferred embodiments.

With reference to FIG. 26, spacers 175 can be formed as discussed withrespect to FIGS. 2-13 above. The spacers 175 can formed of, e.g.,silicon oxide. It will be appreciated that the spacing and size of thespacers 175 can be determined with reference to the spacing and size ofthe features in the mask pattern to be formed (FIGS. 32 and 33). Forexample, where the mask features to be formed are 25 nm in width andhave a regular spacing of about 25 nm or less, the spacing betweenspacers 175 can be about 175 nm or more, to allow for 3×25 nm featuresbetween the spacers 175 and 4×25 nm spaces between the features and thespacers and between each pair of the features. Given features with suchsmall widths, ALD is preferably used to deposit the layers of materialwhich will form the features, as discussed below. It will be appreciatedthat the spacers 175 can be spaced to accommodate more or fewer than 3features and 4 spaces.

A layer 400 is then deposited on the spacers 175 and the hard mask layer150, as shown in FIG. 27. The layer 400 is formed of a material that canbe selectively etched relative to the spacers 175 and that can bedeposited with good conformality, uniformity and step coverage. If thefeatures 175 comprise silicon or silicon oxide, the layer 400 can be,e.g., silicon nitride that is deposited by ALD. The thickness of thelayer 400 is preferably equal to the desired width between mask featuresin the later-formed mask (FIGS. 32 and 33).

With reference to FIG. 28, a layer 410 is deposited on the layer 400.The layer preferably comprises the same or similar material, e.g.,silicon oxide, as the spacers 175. The layer 410 is preferably depositedby ALD for high conformality, uniformity and step coverage. The layer410 preferably has a thickness substantially equal to a desired width oflater-formed mask features (FIGS. 32 and 33). The layer 410 is thensubjected to a spacer etch using, e.g., a fluorocarbon plasma, to formspacers 475, as shown in FIG. 29.

With reference to FIG. 30, a layer 420 is deposited over the structureof FIG. 29. For simplicity in processing, the layer 420 preferablycomprises the same material, e.g., silicon nitride, as the layer 400 andis preferably deposited by ALD. The thickness of the layer 420 ispreferably equal to a desired spacing of the mask features (FIGS. 32 and33).

With reference to FIG. 31, a layer 430 is deposited. The layer 430preferably is formed of the same material, e.g., silicon oxide, as thespacers 175 and is preferably deposited by ALD or another process thathas good gap fill characteristics.

It will be appreciated that the layers 400-430 follow the contours ofthe spacers 175 and the layers 400-420 preferably each has a thicknessless than the height of the spacers 175. As a result, each of thelayers, as-deposited, has a horizontally extending portion. As shown inFIG. 32, the entire structure can be planarized to leave a portion ofeach of the layers 400, 420 and 430 and the spacers 475 exposed. Theplanarization can be achieved by, for example, CMP.

With reference to FIG. 33, the planarized structure is subjected to ananisotropic etch which is preferably selective for the material formingthe layers 400 and 420. For example, where the layers 400 and 420 aresilicon nitride, a suitable etch chemistry includes a CF₄, CHF₃, NF₃,C₃F₆ and/or C₄F₈-containing plasma. Parts of the structure unprotectedby silicon oxide parts 175, 430 and 475 are etched, leaving behind apattern of features defined by the parts 175, 430 and 475. It will beappreciated that the height of the spacers 175 is chosen such that eachof the parts 475, 420 and 430 have vertically extending portions thatare sufficiently tall to allow the planarization process to exposesurfaces of those portions while leaving those portions sufficientlytall to effectively transfer patterns to underlying layers via etching.

The pattern defined by the parts 175, 430 and 475 can then betransferred to the hard mask layer 150 by etching the layer 150 throughthat pattern, using, e.g., a HBr and Cl₂-containing plasma etch. Whereetches highly selective for the substrate 110 relative to the hard masklayer 150 are available, the hard mask layer 150 can be used as a maskto etch the substrate 110. In other embodiments (FIGS. 34-35), thepattern in the hard mask layer 150 can be transferred to another layer,which is then used as the primary masking layer for patterning thesubstrate 110. As noted above, an exemplary sequence of layers isillustrated in FIG. 34 and is discussed in U.S. Patent ProvisionalApplication No. 60/662,323 to Tran et al., filed Mar. 15, 2005, entitledPitch Reduced Patterns Relative To Photolithography Features, AttorneyDocket No. MICRON.316PR (Micron Ref. No. 2004-1130.00/US), the entiredisclosure of which is incorporated herein by reference. With referenceto FIG. 35, the pattern in the hard mask layer 150 can be transferred tothe layer 155, and from the layer 155 to the layer 160. The layer 160preferably can be etched with good selectivity relative to materials inthe substrate 110, particularly when multiple materials are exposed bythe mask, and is used as the primary masking layer. Consequently, evenwhere overlying layers may be etched away in the course of patterningthe substrate 110, the layer 160 still remains to complete thepatterning process.

Thus, it will be appreciated that mask patterns formed according to thepreferred embodiments offer numerous advantages. For example, becausethe formation of mask features is decoupled from the determination ofthe spacing of the lines, very closely spaced features can be formed. Ifdesired, the spacing between these features can be smaller than theresolution limit of photolithographic techniques used to pattern themask features. Moreover, precision in spacing these mask features can beimproved, since photo-overlay capabilities can be more precise thanphotolithographic techniques in aligning features and since theformation of features on overlying levels allows active correction ofany misalignments via, e.g., measurement of feature positions and trimetches.

In addition, deposition techniques such as CVD and ALD allow goodcontrol over the thickness of deposited layers. Thus, using thethickness of deposited layers to determine feature spacing also allowsfeatures to be formed with small and precisely defined spacing.Moreover, errors in positioning and spacing caused by photo-misalignmentcan be minimized, since photolithography is preferably used only in aninitial step for defining spacers.

It will be appreciated that while discussed with reference to particularmaterials for the various layers and parts discussed herein, othermaterials can also be used. Preferably, however, any other materialsthat may be used offer the appropriate etch selectivity relative to thematerials that are used, as discussed above.

In addition, the masks discussed herein can be used to form variousintegrated circuit features, including, without limitation, interconnectlines, landing pads and parts of various electrical devices, such ascapacitors and transistors, particularly for memory and logic arrays inwhich dense repeating patterns are desirable. As such, while illustratedas lines with regular spacing and regular widths for ease ofillustration, the masks can have features with variable spacing andvariable dimensions. For example, with reference to FIG. 23, the spacers275 on the second level can be formed overlapping the spacers 175 toform a large feature (e.g., a landing pad), can be spaced differentlyfrom each of the spacers 175 and 375, can be occur at irregularintervals, can have a different width from the spacers 175 or 375, etc.Also, more than three levels of spacers may be formed, depending upon,for example, the spacing of the spacers 175, 275 and 375, and whetherthe spacers 275 or 375 occur irregularly, leaving room at some placesfor other mask features to be formed. The spacers 175 (FIGS. 13 and 26)and 275 and 375 (FIG. 23) can also be more than pitch doubled. Anexemplary method for further pitch multiplication is discussed in U.S.Pat. No. 5,328,810 to Lowrey et al. with reference to FIGS. 19-23 ofthat patent.

In other embodiments, wither reference to FIGS. 13 and 26, rather thanremoving some spacers 175 on every level, the spacers can be formedhaving a separation (using a wide mandrel) that is wide enough toaccommodate other spacers 275, 375 or mask features 430, 475 in thatseparation. In other words, paired spacers 175 can be formed having theseparation of the “single spacers.” In addition, if the spacers 175 havea critical dimension that is within the capabilities of the technique,e.g., photolithography, the used to define the mandrels 124 b (FIG. 7),the spacers 175, 275, 375 on each level can be replaced by, e.g.,photolithographically defined features. For example, thephotographically defined features can be transferred to a layer ofamorphous carbon and then to a layer of the same material as the spacers175, 275, 375. The layer can be formed of, e.g., silicon oxide, to formsilicon oxide features on a first level. An amorphous carbon layer, ahard mask layer and a photoresist can then be sequentially overlaid thesilicon oxide features to form additional mask features on another levelover the silicon oxide features. This process can be repeated to formadditional features. By using photo-overlay techniques to position theadditional mask features, the spacing between the mask features can bemade smaller than the resolution limits of the photolithographictechnique used to define the features.

The preferred embodiments can be employed multiple times throughout anintegrated circuit fabrication process to form features in a pluralityof layers or vertical levels, which may be vertically contiguous ornon-contiguous and vertically separated. In such cases, each of theindividual levels to be patterned would constitute a substrate 110. Inaddition, some of the preferred embodiments can be combined with otherof the preferred embodiments, or with other masking methods known in theart, to form features on different areas of the same substrate 110 or ondifferent vertical levels.

Accordingly, it will be appreciated by those skilled in the art thatthese and various other omissions, additions and modifications may bemade to the methods and structures described above without departingfrom the scope of the invention. All such modifications and changes areintended to fall within the scope of the invention, as defined by theappended claims.

1. A method for forming an integrated circuit, comprising: forming aplurality of spacers of a first material; covering the spacers bydepositing a layer of a second material on the spacers, wherein athickness of the layer is less than a height of the spacers; depositinga layer of a third material on the layer of the second material; andremoving parts of the layer of the second material immediately adjacentthe spacers.
 2. The method claim 1, further comprising performing aspacer etch on the layer of the third material to form spacers from thelayer of the third material.
 3. The method claim 1, further comprisingdepositing a layer of a fourth material on the layer of the thirdmaterial, wherein parts of the layer of the fourth material extend belowthe height of the spacers.
 4. The method claim 3, further comprisingdepositing a layer of a fifth material on the layer of the fourthmaterial, wherein parts of the layer of the fifth material extend belowthe height of the spacers.
 5. The method claim 4, wherein each of thesecond material, the third material, the fourth material and the fifthmaterial are deposited by an atomic layer deposition.
 6. The methodclaim 4, further comprising performing a planarization process to exposesurfaces of each of the layer of the second material, the layer of thefourth material.
 7. The method claim 6, wherein performing theplanarization process further exposes each of the spacers, the layer ofthe third material and the layer of the fifth material.
 8. The methodclaim 6, wherein exposing surfaces comprises performing a chemicalmechanical polishing process.
 9. The method claim 6, further comprisingselectively etching exposed surfaces of the layer of the second materialand the layer of the fourth material to form a mask pattern.
 10. Themethod claim 1, further comprising transferring the mask pattern tolayer of material underlying the spacers.
 11. The method claim 1,further comprising transferring the mask pattern to a substrateunderlying the spacers.
 12. The method claim 1, wherein forming theplurality of the spacers comprises: forming a plurality of mandrels;forming spacers on sidewalls of the mandrels; and selectively removingsome of the spacers to leave spacers on only one sidewall of each of theplurality of mandrels.
 13. The method claim 1, wherein the firstmaterial, the third material and the fifth material are each selectivelyetchable relative to the second and the fourth materials.
 14. The methodclaim 13, wherein the first material, the third material and the fifthmaterial are the same material.
 15. The method claim 14, wherein thesecond material is the same as the fourth material.
 16. The method claim1, wherein a critical dimension of each of the first and the secondplurality of spacers is about 25 nm or less.
 17. The method claim 16,wherein a lateral separation between each of the spacers and featuresformed of the third material, after removing parts of the secondmaterial, is about 25 nm or less.